Incompleteness of combustion processes is betrayed by the presence of combustibles in the products of combustion, i.e. of combustible gases determining the amount of chemical incomplete combustion of fuel and of solid particles of fuel indicating the amount of unburned carbon.
The two factors mentioned are attributed to feeding the fuel and oxidizing agent at a ratio other than the specified one, deviating from a specified procedure of preparing the fuel and oxidizing agent, poor uniformity of intermixing thereof, failure to observe a specified optimal temperature condition of combustion. An inadequate construction of the furnace used may also lead to incomplete combustion and unburned carbon. A remedy enabling these drawbacks to be eliminated partially of fully is either an effective control of combustion or a reconstruction of the furnace.
The presence of said drawbacks can be established by monitoring--with a requisite accuracy and in good time--the degree of incomplete burning as defined by the content of combustibles in the end products of fuel combustion.
The determination of the unburned carbon, which is the source of fuel loss with the slag and effluent gas, invites significant difficulties. Varying with the operating conditions such as the milling fineness of fuel particles, the way the fuel is being mixed with the oxidizing agent, the temperature of the process, etc., the unburned carbon is quantitatively defined by the carbon content of the ash residue where carbon is present in the form of reluctantly-burning coke particles.
At present, the content of combustibles in the ash residue is determined mainly at the laboratory from the loss in the weight of an ash sample after reburning same in a muffle furnace. Recurrent monitoring on these lines, the result of which remains unknown for several hours after a sample has been taken, fails to provide for an effective combustion control in good time. As a result, unburned fuel can be carried away with the products of combustion during an interval of time sufficiently long to cause excessive fuel consumption.
The problem of a more effective combustion control has been tackled so far to some extent only.
There is known a method of determining the content of combustibles in the end products of fuel combustion (cf., for example, USSR Inventor's Certificate No. 391,355, Cl. F 23 N 5/24) according to which a sample of end products of fuel combustion is introduced into the space between the plates of a capacitor. The resulting change in the capacitance defines the dielectric constant of the sample and the changes in the dielectric constant indicate the content of carbon in the end products of fuel consumption.
However, this method of determining the content of combustibles lacks accuracy, for various metal oxides present in the ash residue as well as moisture and other admixtures present in the sample distort the results of measurements.
Also known is an apparatus for determining the content of combustibles in the end products of fuel combustion (cf., for example, USSR Inventor's Certificate No. 375,449, Cl. F 23 N 5/24) incorporating a sampler, a sample separator setting apart the coarse fraction for the analysis, an electrically-driven screw feeder feeding the sample for the analysis, a capacitor connected into a measuring circuit and used to introduce the sample between its plates, and a meter.
The elimination of the small fraction from the sample in the known apparatus impairs the representativeness of the sample. Foreign matter present in the sample and variations in the concentration of the components of the ash residue also influence the accuracy of measurements.
Closer than anything else to the disclosed method in point of technical essence is a known method of determining the content of combustibles in the end product of fuel combustion consisting in taking a sample of the end products of fuel combustion, introducing the sample into a heating zone of an electric heater, heating the sample in the presence of an oxidizing agent to a temperature equal to or greater than the fire point of the combustibles contained therein which, consequently, inflame and finding the content of combustibles from the amount of heat liberated during the combustion, measurements of the temperature in the zone of heating--which varies directly with said amount of heat--being taken to that end (cf. an article "Ustroistva dlya opredeleniya poter's mekhanicheskim nedozhogom topliva" by Popov K. N., Agafonov E. V. and Matonin L. N., in Russian, in the monthly "Elektricheskie stantsii", No. I, 1973).
The known method also lacks accuracy, especially in the case of a continuous determination of the content of combustion in samples fed without interruption, for any change in the temperature influences the amount of heat lost into the surroundings and with the end products of combustion.
Further known is an apparatus for determining the content of combustibles in the end products of fuel combustion which realizes the known method referred to above. Said apparatus incorporates an oven with electric heaters, a pipe which is connected to a sampler and serves to introduce a sample of the end products of fuel combustion and pipes for feeding an oxidizing agent and removing the end products of combustion of the combustibles. The amount of heat liberated during the combustion of the combustibles is determined with the aid of temperature transducers (thermocouples) provided in the heating zone of the apparatus.
A changing temperature of the sample and structural members of the oven influences the amount of heat escaping into the surroundings with the end products of combustion. Some of the heat accumulates in the structural members of the oven in the heating zone. This all results in a disproportion between the heat liberated due to the combustion of the combustibles and the changes in the temperature. Apart from that, the temperature level used as reference in reading the changes in the temperature may shift, rendering the determination of the content of the combustibles more inaccurate. The known apparatus also lacks reliability, for any possible increase in the content of combustibles may cause a rise of the temperature in the heating zone to a point detrimental to the electric heater and leading to slagging of the oven.